1. Field of the Invention
The present invention relates to a method of determining a value of density of a heat absorbing agent, a method of forming a three-dimensional object, an apparatus for forming a three-dimensional object, a non-transitory computer readable recording medium having stored thereon a program for determining a value of density of a heat absorbing agent, and a non-transitory computer readable recording medium having stored thereon a program for forming a three-dimensional object.
2. Description of the Related Art
A conventional three-dimensional printing technique based on a three-dimensional formation method has been put to practical use in a printing in braille, an UV-ink over-glazing, a physical extruding, and a three-dimensional printer. For example, a method using a thermal-expansion sheet to form a three-dimensional image has been proposed by Japanese Unexamined Patent Publication No. Sho54-089638. When applied with a heat treatment, the thermal expansion sheet distends and expands its volume. The formation method applies irradiation light equally over the thermal-expansion sheet with an image printed thereon, and the printed image portion selectively receives heat and rises depending on difference in a light absorption rate, whereby the three-dimensional image is distended.
The conventional three-dimensional image forming method disclosed in Japanese Unexamined Patent Publication No. Sho54-089638 includes a lot of troublesome processes which need much time to produce a three-dimensional image printing. Therefore, this method invites various problems including an increased cost. Further, in the three-dimensional image forming method, the image is formed at first and then the image portion is heated and expanded its volume. Therefore, the external surface of the expanded image portion causes crack, resulting in deterioration in the quality of the three-dimensional image.
To solve these problems involved in the conventional technique, an apparatus, a system and a method for producing a three-dimensional printed-matter of desired parts of an image which are made cheap and of high quality in a simple manner, have been proposed by Japanese Unexamined Patent Publication No. 2012-171317.
The three-dimensional image printing method based on the techniques disclosed in Japanese Unexamined Patent Publication No. 2012-171317 includes processes of producing a solid on a thermal-expansion recording medium as illustrated in FIG. 12A to FIG. 12G, for example, based on the fundamental concept of producing a solid on a thermal-expansion recording medium as illustrated in FIG. 11A, FIG. 11B and FIG. 11C.
The three-dimensional image printing method will be described briefly. FIG. 11A is a view showing a structure of the thermal-expansion recording medium. FIG. 11B is a view for explaining the principle of the process of selectively heating apart of the thermal-expansion recording medium to make thermal expansion. FIG. 11C is a cross sectional view showing the thermal-expansion recording medium which has been subjected to the process shown in FIG. 11B.
As shown in FIG. 11A, the recording medium 1 consists of a substrate 2 and a distending resin layer 3 containing a thermal expansion agent, coated on the substrate 2. As the recording medium 1 consisting of the substrate 2 and the distending resin layer 3, goods available on the market can be used.
For example, an electro-photographic type image forming apparatus is used to print a solid black image 4 with black toner on a portion of the distending resin layer 3 of the recording medium 1, which portion is to be distended or to be made three-dimensional, and the portion, on which the solid black image 4 has been printed is heated by a heater 6 of a heating device 5, as shown in FIG. 11B.
The heating device 5 is composed of (1) a loading table 7 with a pair of parallel guide grooves 8, 8 formed along its both sides, (2) a pair of heater supports 9, 9 which reciprocally move along the guide grooves 8, 8, and (3) the heater 6 supported between the pair of heater supports 9, 9. The heater 6 radiates heat radiation line onto the surface of the distending resin layer 3 of the recording medium 1 received on the loading table 7, while the heater supports 9, 9 are reciprocally moving along the guide grooves 8, 8.
When the solid black image 4 of black toner receives the heat radiation line, the thermal forming agent contained in the distending resin layer 3 expands with heat to form the expanded portion “G” at the portion where the solid black image 4 of black toner has been printed, as shown in FIG. 11C.
When the recording medium 1 is heated by the heater 6, only the thermal forming agent contained in the portion “G” expands to make a three-dimensional portion, since the heat absorption efficiency of the portion “G” which is printed with black toner is higher than a portion “H” which is not printed with black toner.
FIG. 12A to FIG. 12G are views for explaining a three-dimensional image printing process subjected on the thermal-expansion recording medium. At first, a parked motor tricycle 12 is shot with street trees 11a, 11b in the background, as shown in FIG. 12A, whereby a digital image of the motor tricycle 12 is obtained. The motor tricycle 12 and the street trees 11a, 11b are clipped from the digital image, as shown in FIG. 12B.
The clipped images 11a, 11b and 12 are converted to a sheet of solid black image 13, as shown in FIG. 12C. The solid black image 13 is printed on the surface of the distending resin layer of the recording medium 1, as shown in FIG. 12D. Receiving the heat radiation line 14 from the heater 6, the solid black printed portions expand, as shown in FIG. 12E. A solid white image 16 is printed all over the front surface of the recording medium 1, as shown in FIG. 12F. Then, a full color image is printed on the recording medium 1 based on the original image data, whereby a three-dimensional image is produced, as shown in FIG. 12G.
The three-dimensional image formed in the above described manner has two street trees 11a, 11b and the motor tricycle 12. Although not clearly seen from FIG. 12G, these street trees 11a, 11b and the motor tricycle 12 project from the surroundings. The image is printed on the recording medium with the projections formed thereon, and therefore no crack is caused around the projections of the recording medium 1.
In the three-dimensional image printing method disclosed by Japanese Unexamined Patent Publication No. 2012-171317, the portions of a thermal-expansion sheet which are to be distended are printed with heat-absorbing black ink and all over the surface of the thermal-expansion sheet is heated by a halogen lamp. As a result, the heat is conducted to the surroundings (white portions) of the black printed portions and the surroundings (white portions), on which no black ink is printed, are made to distend and expand. This phenomenon is called an “abnormal expansion”.
FIG. 13A to FIG. 13C are views showing examples of the “abnormal expansion”. FIG. 13A is a view showing a Kanji (Chinese character used in Japanese writing) of “” printed in black ink on the thermal-expansion sheet. When the thermal-expansion sheet with the Kanji of “” printed thereon is heated, the surroundings (white portions) of the Kanji of “” are also heated together with the portion where the Kanji of “” is printed in black, and are subjected to the “abnormal expansion”, whereby the portions close to each other, as indicated by plural arrows “b”, are connected together, as illustrated in FIG. 13B.
FIG. 13C is a view schematically illustrating that the portions close to each other are connected together. The view of FIG. 13C shows that the portions where the Kanji of “” is printed in black and the portions indicated by double-headed arrows have been subjected to the “abnormal expansion”. No measures have been proposed for solving the inconvenience caused by the “abnormal expansion”.